The invention relates generally to optical communication systems, and, more particularly, to an optical switching node and method for operating same.
Optical communications systems are used throughout the world for carrying large amounts of data and voice transmissions. Optical communication systems generally employ fiber optic cables that carry optical signals from one location to another. Typically, many optical signals are carried on a single optical fiber by using wavelength-division multiplexing (WDM). Switching nodes are located along many optical communication paths and are typically connection points for a plurality of optical fibers. The switching nodes include optical and electrical switching equipment. If a particular optical signal on an optical fiber is destined for a particular switching node, the wavelength-multiplexed optical signals on the fiber are demultiplexed at that node into individual optical signals, the individual optical signals are converted by an optical receiver at the node to respective electrical signals, the electrical signal derived from the desired optical signal is switched electronically to its final destination, and a new optical signal is derived from the electrical signal.
In most optical communication networks, many of the optical signals entering a switching node merely pass through the node on the way to their final destination. These optical signals that are destined for a different switching node may require regeneration, equalization and/or wavelength conversion, or may be of the appropriate wavelength, have sufficient optical power and have sufficient signal quality to be communicated directly to the next switching node.
Regeneration is the process of determining whether each bit of the digital signal with which an optical signal is modulated is a binary xe2x80x9conexe2x80x9d or a binary xe2x80x9czero,xe2x80x9d and using this information to create a new, noiseless, undistorted version of the modulated optical signal. Regeneration typically also includes retiring the modulation to reduce timing jitter. In existing optical communication systems, an optical signal is regenerated by converting the optical signal to an electrical signal, processing the electrical signal, and converting the processed electrical signal back to a noiseless, undistorted, jitter-free optical signal for retransmission.
Wavelength conversion involves changing the optical carrier wavelength of an optical signal, without altering the information modulated on the optical signal. Wavelength conversion typically also includes the above-mentioned regeneration process, which will be assumed for the remainder of this document.
Equalization is the process of adjusting the power of an optical signal so that all signals in a system are maintained at the same power level. Equalization is necessary in systems in which optical signals experience different gain or loss as they travel through the system, and is often necessary in WDM systems because of wavelength-dependent loss or gain. Equalization can be performed using a variable optical attenuator.
In existing optical communication systems, all optical signals received at a switching node are wavelength-demultiplexed, if necessary, converted from an optical signal to an electrical signal, and regenerated. Some advantages of such existing switching nodes are that wavelength conversion (which eases network management) and equalization are straightforward; and that electronic logic can be used to monitor the quality of the incoming signals so that upstream faults can be rapidly and precisely identified and compensated.
However, such existing switching nodes receive, demultiplex, regenerate and retransmit some signals that are destined for a different switching node and that do not require regeneration, equalization or wavelength conversion. Therefore, because existing switching nodes must contain sufficient resources to operate on all optical signals present at the switching node, such existing switching nodes contain more expensive resources (wavelength demultiplexers and multiplexers, receivers, transmitters, regeneration and monitoring logic) than might be necessary.
Therefore, it would be desirable to have a switching node that minimizes the amount of signal processing performed at the node such that only signals that require processing are processed by the node. Such a switching node would allow an optical signal that is destined for a different node and that requires no regeneration, equalization, wavelength conversion or interchange with other signals having the same wavelength to remain as an optical signal as it passes directly through the switching node. The cost of such a switching node could be less than the cost of an existing node having similar switching capacity because it could contain fewer wavelength demultiplexers and multiplexers, receivers, transmitters, regeneration and monitoring logic, etc.
The invention provides an optical switching node and method for operating same. In architecture, the invention may be considered an optical switching node comprising a fiber cross-connect that receives optical signals and a node controller in communication with the fiber cross-connect.
The node controller is configured to determine whether any of the optical signals are destined for a different optical switching node. The node controller is also configured to determine whether any of the optical signals destined for the different switching node require further processing. The optical switching node also includes a signal converter that operates in response to the node controller and converts to an electrical signal only those optical signals destined for the optical switching node and those optical signals destined for the different optical switching node that require further processing.
The invention can also be conceptualized as a method for operating an optical switching node. The method comprises the steps of determining whether any of the optical signals received at the optical switching node are destined for a different optical switching node and determining whether any of the optical signals destined for the different switching node require further processing. Only the optical signals determined to be destined for the optical switching node or to be destined for the different optical switching node and require further processing are converted to electrical signals.
The invention has numerous advantages, a few which are delineated below merely as examples.
An advantage of the invention is that it reduces the complexity of a switching node.
Another advantage of the invention is that it reduces the cost of an optical switching node.
Another advantage of the invention is that it allows the direct passage of an optical signal through a switching node.
Another advantage of the invention is that it reduces the amount of resources (wavelength demultiplexers and multiplexers, receivers, transmitters, regeneration and monitoring logic) that are necessary at an optical switching node.
Another advantage of the invention is that it is simple in design and easily implemented on a mass scale for commercial production.
Other features and advantages of the invention will become apparent to one with skill in the art upon examination of the following drawings and detailed description. These additional features and advantages are intended to be included herein within the scope of the invention.